An angular rate sensor, also referred to as a gyroscope, senses angular speed, rate, or velocity, also referred to as angular rate of rotation, around one or more axes. Commonly, angular rate sensors are microelectromechanical systems (MEMS) devices manufactured using MEMS technology, which provides a way to make very small mechanical structures and integrate these structures with electrical devices on a single substrate using conventional batch semiconductor processing techniques. MEMS angular rate sensors are widely used in applications such as automotive, inertial guidance systems, gaming systems, smartphones, cameras, etc.
Some prior art MEMS angular rate sensors utilize multiple vibrating structures or masses that are suspended over a substrate. Such MEMS angular rate sensors are often referred to in the art as vibrating structure gyroscopes or Coriolis vibratory gyroscopes. One type of vibrating structure angular rate sensor is a “tuning fork” angular rate sensor having multiple masses, also referred to herein as Coriolis masses. In operation, at least some of the Coriolis masses, acting as drive masses, are driven to resonance in opposite directions, also referred to herein as anti-phase. In response to an external angular stimulus about an input axis, at least some of the Coriolis masses, acting as sense masses, move in phase opposition by exploiting a Coriolis acceleration component, also referred to in the art as the Coriolis effect. Namely, antiphase movement of the sense masses in response to the Coriolis effect has an amplitude that is proportional to the angular rate of rotation of the angular rate sensor about the input axis.
A drawback of angular rate sensors is their susceptibility to common mode excitation of the Coriolis masses in response to linear and/or angular acceleration due to an external stimulus such as shock, vibration, spurious or parasitic acceleration, etc. Common mode excitation, also referred to herein as in-phase motion, is a condition in which the Coriolis masses, operating as drive masses, sense masses, or both, move in the same direction and at the same amplitude and at a frequency (i.e., the common mode frequency) that is as low as or lower than an operating frequency of the angular rate sensor (i.e., the differential mode frequency). Common mode excitation can lead to inaccuracy or complete failure of the angular rate sensor.